The present invention relates to an apparatus and method for monitoring the state of opening of a control valve of a coolant circuit of a combustion engine. More specifically, this invention has to do with a method of a control valve of a coolant circuit of a combustion engine, with the control valve having a valve element that is actuatable by an actuator for enabling and/or blocking a coolant flow in the coolant circuit which has a heat exchanger (e.g., a radiator), and having a device for detecting the position of the valve element for monitoring the opening state of the control valve.
The invention also relates to a device for carrying out the method, the device including a thermostatic valve having a valve plate displaceable by means of a spring-loaded positioning element in the coolant passage to or from a heat exchanger of a coolant circuit of a combustion engine, and having a wax element to which heat is applicable by means of an electrically actuatable heating element and which actuates the positioning element, and having a sensor which detects the travelling distance of the valve plate and/or positioning element by contactless means, and with a device for comparing an actual value of the travelling distance with a target value of the travelling distance.
Combustion engines are usually operated with a coolant circuit having a heat exchanger, by means of which the waste heat resulting from the combustion that is not required for the interior air conditioning of the combustion engine-powered vehicle can be released into the environment. If the combustion engine, or car engine, is started, i.e. transferred from the non-powered state into the powered state, the engine undergoes a warm-up process, which should be kept as short as possible.
The motor is thus started, for example, at a coolant temperature which corresponds to the ambient temperature and the temperature of coolant flowing through the engine which can be measured, for example, at the coolant outlet region or another measuring point of the engine by means of a sensor, then increases according to a heating curve, which depends, for example, on the load demanded of the engine.
The coolant circuit of the motor contains a control valve, commonly designated as a thermostat or thermostat valve, which has a valve element in the form of a valve plate or similar, and is provided for controlling the passage of the coolant present in the coolant circuit as it flows through the heat exchanger. During the warm-up phase, the valve element is designed to prevent the flow of coolant through the heat exchanger, the so-called large coolant circuit which comprises the heat exchanger, in other words to keep it closed so that coolant only flows through the so-called small coolant circuit, which comprises the circulation channels of the engine for the flow of coolant through the engine block and cylinder head, and one or more heat exchangers for air conditioning of the vehicle interior.
It is the task of the engine's thermal management system, exercised by a control device such as the engine control unit, to control the heat transport using the coolant regulation system. The thermal management system is designed to ensure on the one hand, sufficient interior air-conditioning of the vehicle and on the other hand to rapidly warm up the engine, in order to reduce pollutants emitted in the combustion during the warm-up procedure and to keep the engine wear caused by cold running of the engine as low as possible.
During the warm-up process therefore, the control valve or thermostatic valve plays an essential role, and its state of opening for the period of time required by the warm-up process is crucial. The control valve is designed to keep the large coolant circuit closed below its intended operating opening temperature, which varies greatly from engine to engine, and thus prevent the dissipation of heat via the heat exchanger during the warm-up process, which contributes to emissions. The polluting emissions of a vehicle type can be a criterion relevant to type approval, and therefore it can be a requirement to monitor the proper functioning of the control valve during operation of the vehicle, for example using the existing diagnostic equipment in the vehicle, i.e. equipment for on-board diagnostics (OBD diagnosis).
The diagnosis of the thermostat is intended to test the heating behaviour of the coolant to determine whether the engine will reach its operating temperature in a reasonable period of time. The correct functioning of the thermostatic valve or control valve is therefore to be monitored and any malfunctions identified.
A malfunction is deemed to be present, inter alia, if the temperature of the coolant has not reached a minimum temperature within a reasonable time, the temperature being stipulated for other vehicle-specific OBD diagnostic procedures. A malfunction is also deemed to exist if the measured coolant temperature does not reach the operating opening temperature of the control valve.
According to a method known by one of the applicants, the function of the control valve in the cooling circuit is monitored by measuring the temperature of the coolant at the coolant outlet region of the engine by means of a coolant outlet sensor. The measured temperature TMot is compared with a modelled coolant engine temperature, which uses the air mass flow rate as a criterion for the engine load, the ambient temperature as a correction value, and the coolant outlet temperature measured when starting the engine as the starting value for an iteration and as the current modelled coolant engine temperature. Plotted against time, the characteristic curve of the modelled coolant engine temperature for a control valve which is functioning as intended lies a short distance below the actual temperature characteristic of the control valve.
The known method starts after the combustion engine is started, i.e. after the operational state of the combustion engine changes from the non-powered state into the powered state, and determines (inter alia) the modelled temperature as a function of the measured air mass flow and compares this temperature with the actual coolant temperature measured at the coolant outlet area, or any other suitable sensor measuring point, by forming a difference. If the delta between the measured and the modelled temperature is greater than a predefined threshold value, an error bit is set, since the actual measured temperature deviates substantially from the modelled temperature and this is an indication that the control valve is not fully closed at the time at which the coolant is only supposed to flow through the small coolant circuit, which means the situation is that of a control valve which is stuck in the open position.
Such a control valve sticking in the open position causes, due to the dissipation of heat via the heat exchanger to the vehicle environment, that the time required for the warm-up procedure is much longer than the time required by a control valve functioning as intended. This results that the emission of pollutants is greater than the emissions occurring in a control valve functioning as intended. The on-board diagnostic system (OBD system) of the vehicle acknowledges the fault and the driver of the vehicle may be informed by means of an optical signal in the form of a maintenance indication to eliminate the cause of the fault, a control valve sticking open, possibly after reading from the vehicle-internal fault memory.
Although the foregoing method is the one best proven in practice, it has room for improvement. This known method requires the engine to be started for the purpose of measuring the air mass flow rate, and a minimum energy input into the engine coolant for measuring the actual coolant temperature during the warm-up phase, which is limited by an upper temperature threshold value of the coolant of, for example, 80° C.
In patent document DE 199 60 190 A1 a control valve for a control circuit has been disclosed, which can be a coolant circuit of a combustion engine. The control valve has a valve element, which can be adjusted by way of an electric direct current motor or a proportionally acting electromagnet. The position of the control valve can be detected by means of a position measuring device, which has the facility for inductive, capacitive or magnetic distance measurement.